1. Field of the Invention
The invention relates to methods for treating mixtures of alkyl substituted phenols so that they will not cause discoloration when used in epoxy resins and more particularly relates to methods of treating mixtures of alkyl substituted phenols by means of the addition of N,N-diethylhydroxylamine.
2. Description of Other Related Methods in the Field
Many decolorizing agents now in use remove color by physical adsorption. The most common materials to remove color by this means are represented by charcoals, blacks (such as carbon black), clays and earths. Other compounds remove color by chemical reaction and are frequently more specific as to the materials they can remove color from than the physical adsorption agents. While attempts have been made to predict compound colors, such as by electronegative or steric contributions of substituents to aromatic rings, numerous exceptions to rules relating color to structure require color prediction to be based largely on empirical observations, see Griffiths, John; Colour and Constitution of Organic Molecules; London: Academic Press (1976), pp. 89-90. As a result, attempts to remove color from a specific compound tend to be strictly trial and error operations.
Specific examples may be seen in the decolorization of amines. U.S. Pat. No. 3,723,529 describes the decolorization of polyethylene polyamines through the use of a heated activated carbon treatment. The decoloration of ethylene amines may also be accomplished by heating the ethylene amines with zinc, aluminum or tin, or a combination thereof together with sodium hydroxide and/or potassium hydroxide according to the method described in Japanese Kokai 69-2209.
Activated carbon is frequently used as a method for purifying drinking water. Water may also be decolorized and decontaminated by contact with ozone as noted by R. D. Gabovich, et al. in Gig. Sanit. Vol. 34, No. 6, 1969, pp. 18-22 (Chemical Abstracts citation 71:53407k).
Other materials are well known as decolorizers; for example, ion-exchange resins. J. C. Abram, et al., in Sucr. Belge/Sugar Ind. Abstr. Vol. 90, No. 11, 1971, pp. 525-32 (CA 76:128256), describe color removal in substances such as polyethylene glycol and phenol by means of ion-exchange resins. U.S. Pat. No. 3,660,317 discloses that ion-exchange resin beads may be used to decolorize and deodorize materials and absorb ammonia. Ion-exchange resins may also be used to remove the metallic impurities from bis(2-hydroxyethyl) terephthalate by the method described in French Pat. No. 1,566,485 (CA 72:3241). Tertiary-aminocyclobutanes that have electronegative substituents have been found to be useful color stabilizers and antioxidants in gasoline according to U.S. Pat. No. 3,369,024.
A number of methods have been devised for purifying phenols and substituted phenols. For example, U.S. Pat. No. 3,437,699 reveals that phenol may be purified of color-forming impurities by treatment with hydrogen in the presence of a hydrogenation catalyst such as nickel-molybdenum. Mixtures containing o-hydroxybenzoic acids and saturated aliphatic polybasic acids and/or polybasic phosphoric acids or phosphoric acid esters may be added to phenol to give a color-stable product according to French Pat. No. 1,502,518 (CA 70:11340).
Mono- and dicarboxylic acids are effective to prevent the discoloration of phenols such as 2,6-diisopropylphenol according to Netherlands Appl. No. 6,516,378 (CA 67:2878). Compounds somewhat similar to those decolorized by the instant invention are p-tert-butylphenol and nonylphenol which may be decolorized by the addition of small amounts of hydrazine or hydrazine hydrate as described in Japanese Kokai 77-68,134 (CA 87:151841). Urban, et al. in Sb. Pr. Vyzk. Chem. Vyuziti Uhli, Dehtu Ropy, No. 10, 1970, pp. 65-78 (CA 74:22497), note that hydrazine hydrate improved the color stability of mixed monohydric phenols only in the absence of iron. The addition of powdered iron or an iron strip to alkylphenols such as 2,4-di-t-butylphenol and triisopropylphenol prevents coloration as French Pat. No. 1,597,867 discloses (CA 74:76170). Brominating phenols such as 4,4'-isopropylidenediphenol makes products of improved color and purity through the method of U.S. Pat. No. 3,546,302. Further, U.S. Pat. No. 3,454,654 discloses that 2,6-di-t-butyl-4-cresol may be used as a color stabilizer in the dibromination of phenol.
Color removal from substituted phenol polymers, such as poly(2,6-dimethyl-1,4-phenylene ether) may be effected by treating them with a reducing agent such as lithium aluminum hydride, sodium borohydride or sodium hydride as noted in Japanese Kokai No. 71-06,869 (CA 76:114121). Addition of ammonium acetate and other such compounds can decolorize phenol-aromatic hydrocarbon-aldehyde resins as described in Japanese Kokai No. 71-02,897 (CA 76:34873). Further, Japanese Kokai No. 74-31,631 (CA 81:25366) discloses a method of producing p-alkylphenols without color by means of a distillation process. The decolorization of dialkylolalkylphenols, such as 2,6-dimethylol-4-nonylphenol, may be accomplished by adding dilute solutions of oxalic acid as shown in U.S. Pat. No. 3,306,938. Alkylphenol-ethylene oxide adducts and the sulfates thereof may be purified and decolorized by contacting the materials with an alkali metal borohydride as described in U.S. Pat. Nos. 3,375,284 and 3,687,999.
U.S. Pat. No. 4,337,369 teaches a method for eliminating color-causing impurities in mixtures of t-butyl alkylphenols by treatment with trioxane at about 100.degree. C. Finally, another method of decolorizing mixtures of t-butyl alkylphenols, this time by treatment with N-(2-hydroxyethyl)oxazolidine at about 90.degree. C. is described in U.S. Pat. No. 4,356,330 (see also, the references cited in these last two patents).